1. Field of the Invention
This invention relates to the packaging of temperature-sensitive microelectronic devices including semiconductors and hybrid integrated circuits and the like. More particularly, this invention relates to improvd packaging techniques capable of producing hermetically sealed packages with a relatively low rise in the interior package temperature, thereby assuring that the enclosed circuitry is not damaged by heat. In the package to be described, the circuit elements are fabricated on a planar ceramic substrate with a rimless four-sided cover sealed thereto by means of a fused glass frit sealing compound.
2. Description of the Prior Art
A variety of ways have been developed for packaging microelectronic elements. Packaging of IC chips commonly includes the use of conduction-convection or IR furnaces to heat the package components to sealing temperature. The high interior package temperatures that result from use of such a furnace do not injure IC chips which already have been subjected to high-temperature processing including annealing. Such high interior temperatures however are not acceptable for packaging certain other types of microelectronic devices which are quite temperature-sensitive, particularly those incorporating hybrid integrated circuitry, and involving components which are mounted using organic adhesives. Thus, there has been a need for a commercially satisfactory packaging technique which does not raise the internal package temperature significantly, thereby to avoid damage to temperature-sensitive circuit elements.
Prior attempts have been made to solve this problem. For example, reference may be made to Zimmerman U.S. Pat. No. 3,973,388 which shows (see FIGS. 6c-6f) a heater core 58 arranged to be moved into a position surrounding the package lid to apply heat directly by conduction to the rim of the lid. Heat transferred through this rim melts solder which seals the lid to the substrate. Zimmerman provides heat sinks engaged with both the lid and the base to carry off heat with the objective of preventing the interior temperature from rising so high as to damage the packaged circuit elements.
The Zimmerman approach presents a number of problems. First, it is not clear that the package interior will not in practice reach excessively high temperatures for many commercial applications, particularly since the heater core closely surrounds the entire lid and will transfer heat throughout the side wall areas of the lid during the sealing process. Also, the heat is applied only to one side of the interface junction, and proper heating of the solder can be interfered with by camber of the sealing surfaces of either the lid or the base. Moreover, the Zimmerman scheme requires that the lid preferably have a rim, which undesirably takes up valuable space and moreover is difficult to construct with certain types of advantageous materials such as ceramic. In addition, the described technique is not well suited for cost-effective, mass production of electronic components.
Accordngly, it is an object of this invention to provide improved packaging techniques for microelectronic devices. A further object of the invention is to provide a packaging technique, and packages produced thereby, offering hermetic sealing of temperature-sensitive circuit elements with reduced internal temperature during the sealing procedure. Other objects, aspects and advantages of the invention will in part be pointed out in, and in part apparent from, the following description of a preferred embodiment considered together with the accompanying drawings.